Laser photomedicine is a well-established therapeutic modality for a wide variety of conditions. To date, the use of ophthalmic lasers has been limited to either short (around one microsecond or shorter) pulse systems for sub-cellular targeting, or long (hundreds of microseconds and longer) pulse systems that indiscriminately denature relatively large volumes of tissue.
For example, present standard retinal photocoagulative treatment for conditions such as Diabetic Retinopathy, and Age-Related Macular Degeneration utilize visible laser light with exposure durations on the order of 100 ms. Generation of heat due to absorption of visible laser light occurs predominantly in the retinal pigmented epithelium (RPE) and pigmented choriocappilaris, the melanin containing layers directly beneath the photoreceptors of the sensory retina. The RPE is disposed between the sensory retina and the choroid. Due to heat diffusion during long exposures, this standard therapy also irreversibly damages the overlying sensory retina.
Although it does halt the progress of the underlying disease, such irreversible damage decreases the patient's vision by destroying not only the photoreceptors in the irradiated portion of the retina but also by creating permanent micro-scotomas, and possibly also damaging the retinal nerve fibers that traverse the targeted portion of the retina, creating a defect called arc scotoma. Such nerve fiber damage eliminates the signals it would have carried from distal areas of the retina, thus unnecessarily further worsening the patient's vision.
To address these issues, systems and methods for creating spatially confined photothermal lesions in ocular tissues have been proposed, such as in co-pending U.S. patent application Ser. No. 11/606,451, which is incorporated herein by reference. However, what is lacking in such systems and methods is a means for gauging a patient's idiosyncratic response and for reliable delivery of the treatment light to create lesions in response thereto.
Due to strong variability of the retinal absorption, ocular transmission of light, and choroidal blood perfusion, the laser-induced retinal temperature rise strongly varies from patient to patient, and even from location to location in a single patient. So, a global parameter setting for a desired clinical result is not ideal. Left uncorrected, these differences can lead to inhomogeneous treatments, over-treating in some areas and under-treating in others. Physicians have traditionally determined the appropriate treatment for each patient (and even for different areas in the retina of the same patient) by a “trial and error” approach, which takes a significant amount of time and is entirely qualitative.
Accordingly, there is a need for a rapid, robust, and cost-effective system and method for providing predictable ophthalmic photomedical treatment such as, but not limited to, the retina and trabecular meshwork, that is not provided by known methods or devices.